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Date

2016-01-21

Author

Mansfield, Graeme

Type

Thesis

Degree Level

Masters

Abstract

Replacement of fish meal as the primary protein source in diets for farmed carnivorous fish is a major priority for sustainability of the aquaculture industry. Three plant-based protein sources (soybeans, field peas, and canola) were investigated to compare their effects on the health and performance of rainbow trout (Oncorhynchus mykiss) and to identify significant anti-nutritional factors (ANFs). Six separate 8-week studies were conducted, over a period of one year, to assess the effects of protein source and processing level (meal versus protein concentrate) at dietary inclusion rates of 0 to 300 g kg-1.
Abundance of inflammatory and immune marker transcripts including proliferating cell nuclear antigen (PCNA), immunoglobulin M (IgM), interleukin-1 beta (IL-1β), interleukin-8 (IL-8), and interleukin-10 (IL-10) was evaluated in distal intestinal tissue by quantitative PCR (qPCR) analysis. Activity of the pro-apoptotic enzyme caspase-3 was also assayed in distal intestinal tissue. Transcript abundance was highly variable and no suitable genes for the internal normalization of qPCR data could be identified. As a result, transcript copy numbers were reported per 50 ng of total RNA. At 300 g kg-1 inclusion, soybean meal (SBM) increased abundance of IL-8 and IgM, pea meal (PM) increased abundance of IL-10, and canola protein concentrate (CPC) increased abundance of IL-8. Pea protein concentrate (PPC) reduced IL-8 abundance and caspase-3 activity, while increasing abundance of IL-10. Canola meal (CM) and soy protein concentrate (SPC) did not significantly affect the transcript abundance of any assayed gene. Pearson correlation coefficients were determined between gene transcript abundance, performance parameters, protein source, inclusion level, and ANF content. Specific growth rate (SGR) was negatively correlated with the abundance of IL-1β and IgM. Dietary inclusion of SBM was positively correlated with all assayed proinflammatory markers and negatively correlated with SGR. Inclusion of PM was positively correlated with both SGR and the abundance of IL-10. The inclusion of CM was negatively correlated with average daily feed intake (ADFI) and with the abundance of both IL-8 and PCNA. Inclusion of PPC correlated positively with SGR and negatively with the activity of caspase-3. Correlation between transcript abundance and dietary content of putative ANFs suggested negative correlations between glucosinolate content, proinflammatory cytokine expression, SGR, and ADFI; whereas, isoflavone content was positively correlated with proinflammatory markers and negatively correlated with SGR.
In conclusion, although high SBM and CM inclusion levels have been associated with reduced growth performance in trout, only SBM was associated with increased abundance of inflammatory marker transcripts. These contrasting responses may be mediated by CM glucosinolates, which could negatively affect palatability without inducing a pro-inflammatory response. Dietary PM was very well tolerated and may have promoted anti-inflammatory activity. Further processing of protein meals to concentrates markedly reduced any observable negative impact on performance parameters and the abundance of inflammatory marker mRNA transcripts. Interestingly, both PM and PPC were positively correlated with SGR and may contain a beneficial anti-inflammatory component.